This invention relates generally to turbine engines and, more particularly, to apparatus and methods for reducing stress on turbine blades.
Turbine blades include an airfoil, a platform, and a shank. The airfoil has a leading edge and a trailing edge, with the trailing edge being relatively thin in comparison to the leading edge. Typically turbine blades are subjected to high temperature gases by a combustor located upstream from the turbine blades. The airfoil trailing edge region is exposed to such high temperature gases and is prone to failure due to difficulties associated with providing adequate cooling to the region.
To facilitate preventing airfoil failure, a plurality of slots are located in the airfoil trailing edge and cool air is discharged from the slots to cool the trailing edge. These slots sometimes are referred to herein as trailing edge slots.
Turbine engine airfoils are cast with land areas, or ribs, located between the trailing edge slots. The slots are formed by a recessed wall and two steps extend between the recessed wall and an outer surface of the airfoil. The step in the slot located closest to the platform may cause a large stress concentration with high thermal stresses present. The high thermal stresses may result in trailing edge axial cracks which can propagate through the airfoil. Premature failure of the turbine blade may result from the axial cracks. However, the trailing edge slot located closest to the airfoil platform cannot be eliminated because removal would result in trailing edge overheating.
Accordingly, it would be desirable to reduce stress on turbine engine blades in the area where the airfoil trailing edge joins the platform. Additionally, it would be desirable to improve the longevity of turbine blades.